Abstract

Third harmonic generation (THG) in microfibres can be efficiently generated by phase matching the fundamental mode at the pump wavelength with a high order mode at the third harmonic (TH) wavelength at specific microfibre diameters [1]. Similarly, second harmonic generation (SHG) arising from the lack of centrosymmetry at the microfiber surface as well as higher order bulk effects [2], can be optimised by appropriate intermodal pahse matching. Pump power recirculation in a microfibre loop has been proposed as method to improve the THG efficiency [3], as attempts to generate SH and TH in microfibres have shown relatively low efficiency. Yet, the loop mechanical instability remains an issue. Here, we report on using a microknot resonator to recirculate pump light and enhance THG and SHG with high stability and reliability. A strong efficiency enhancement is observed, possibly due to an improved pump coupling in the knot resonator.

© 2015 IEEE